No description available.

My research has focussed on the development of a technique to tailor photochromic switching rates by creating a customised local environment for the dye within an otherwise rigid host matrix. Living radical polymerisation offers the potential to design such a system. A living radical initiator based on a spirooxazine compound was used to polymerise a polymer chain of well controlled molecular weight and polydispersity. This technique facilitated the construction of a conjugate with every photochromic moiety convalently attached to a polymer chain with uniform characteristics. The photochromic behaviour of these new polymer-spirooxazine conjugates were investigated in a cross-linked polymer matrix with a Tg of approximately 120??C. It is well known that photochromic switching is susceptible to local environment effects such as rigidity, free volume and polarity.1, 2 The goal of these systems was to create a uniform local environment which would facilitate controlled changes in the photochromic switching rates. The photophysical investigation of these systems demonstrated the success of this technique. The photochromic rates were directly related to the characteristics of the polymer conjugate. It was postulated the conjugates acted as a customised local environment for the photochromic moiety, encapsulating it from the host matrix. Consequently systematic tailoring of the photochromic switching rates was achieved by changes in the characteristics of the attached polymer. To our knowledge this is the first technique to control local environment of a photochromic compound and thus the first example of systematic tuning of photochromic switching rates. Throughout this research, several characteristics of the attached polymer were modified to give a series of rules for the tuning of photochromic switching rates using this technique. The largest variation in switching speed is achieved through variation of Tg. A range of photochromic rates from extremely slow to near solution-like can be easily achieved. The necessary variations in Tg can be achieved easily using living radical polymerisation techniques. The use of different homopolymers, block and random copolymers were all demonstrated successfully in this work. For finer tuning of the photochromic rates, changes in chain length can be used. It was also found the best living radical polymerisation method for this work was ATRP due to the bulky or incompatible halogen which contributed to efficient encapsulation. However this endgroup effect is only important in systems which do not have a low Tg component. The incorporation of such a component overrides all other contributions to the overall behaviour.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaf 12). Also available via the World Wide Web.

Includes bibliographical references.

My research has focussed on the development of a technique to tailor photochromic switching rates by creating a customised local environment for the dye within an otherwise rigid host matrix. Living radical polymerisation offers the potential to design such a system. A living radical initiator based on a spirooxazine compound was used to polymerise a polymer chain of well controlled molecular weight and polydispersity. This technique facilitated the construction of a conjugate with every photochromic moiety convalently attached to a polymer chain with uniform characteristics. The photochromic behaviour of these new polymer-spirooxazine conjugates were investigated in a cross-linked polymer matrix with a Tg of approximately 120??C. It is well known that photochromic switching is susceptible to local environment effects such as rigidity, free volume and polarity.1, 2 The goal of these systems was to create a uniform local environment which would facilitate controlled changes in the photochromic switching rates. The photophysical investigation of these systems demonstrated the success of this technique. The photochromic rates were directly related to the characteristics of the polymer conjugate. It was postulated the conjugates acted as a customised local environment for the photochromic moiety, encapsulating it from the host matrix. Consequently systematic tailoring of the photochromic switching rates was achieved by changes in the characteristics of the attached polymer. To our knowledge this is the first technique to control local environment of a photochromic compound and thus the first example of systematic tuning of photochromic switching rates. Throughout this research, several characteristics of the attached polymer were modified to give a series of rules for the tuning of photochromic switching rates using this technique. The largest variation in switching speed is achieved through variation of Tg. A range of photochromic rates from extremely slow to near solution-like can be easily achieved. The necessary variations in Tg can be achieved easily using living radical polymerisation techniques. The use of different homopolymers, block and random copolymers were all demonstrated successfully in this work. For finer tuning of the photochromic rates, changes in chain length can be used. It was also found the best living radical polymerisation method for this work was ATRP due to the bulky or incompatible halogen which contributed to efficient encapsulation. However this endgroup effect is only important in systems which do not have a low Tg component. The incorporation of such a component overrides all other contributions to the overall behaviour.

Ormosils (Organically Modified Silicates) have been used in the past as hosts for various organic molecules. In this work, seven different photochromic dyes most of which belong to the spirooxazine / merocyanine family were doped into thin films that were prepared using several increasingly inorganic Ormosil formulations. These dyes were either physically incorporated into the pores of the film or covalently bound to the matrix via a siloxane substituent. The dyes, which undergo a reversible color change upon irradiation, are relatively stable, although they will ultimately degrade after prolonged exposure to ultraviolet irradiation. This work focuses on identifying the variables that influence the rate of dye degradation, including rigidity of the Ormosil matrix, wavelength of irradiation, and the presence of oxygen. The silylated dyes, which are generally regarded as having reduced mobility within the pores of the Ormosil, degraded more slowly, suggesting a link between stability and rotational and translational freedom. Irradiation wavelength also affected dye stability in that limiting exposure to wavelengths in the near UV (and eliminating visible light) causes the least degradation. This is attributed to the photostability of the photomerocyanine isomer. Finally, the presence of oxygen was shown to cause dramatic enhancement in degradation. The mechanisms of each of these effects are discussed.

published_or_final_version / abstract / toc / Chemistry / Master / Master of Philosophy

No description available.

Two-photon photo-activated functional molecules play key roles in a growing number of technological and biological applications as the availability of high powered, tuneable lasers increases. The development of new, strongly two-photon absorbing functional chromophores is key to the advancement of these technologies. A series of photoresponsive compounds including organic chromophores and transition metal coordination complexes were designed, synthesised and characterised by NMR, mass spectrometry, elemental analysis and X-ray crystallography. Photophysical characterisation of the compounds including electronic absorption spectroscopy, luminescence spectroscopy, luminescence lifetime studies and two-photon absorption (2PA) experiments were performed. Density functional theory (DFT) calculations were performed and supporting data are presented. Of particular interest is the use of photochromic materials to address the increasing demand for high-density data storage employing two-photon absorption for 3-dimensional control of excitation. Towards this, a series of four photochromic "push-pull" azobenzenes of donor-pie-acceptor structure containing a para-ethoxy donor substituent have been synthesized with varying strength of the acceptor group (para-NO2, CN, CO2Et, F). Kinetic studies of their one-photon photoisomerisation and thermal cis-trans isomerisation were performed in solution and in polymer films, and their non-linear two-photon trans-cis photoisomerisation was demonstrated. Luminescent metal centres offer the possibility of a fluorescent read-out mechanism for optical data storage, modulated by a photochromic ligand, which may quench fluorescence in one isomer and not the other. Two photochromic pyridyl azobenzene ligands were designed and synthesised and coordinated to Re(I), Pt(II) and Ru(II) polypridyl metal centres. The trans-cis photochromism of the ligands and complexes was investigated by one- and two-photon absorption. Luminescence modulation was demonstrated via photochromism of the coordinated ligand L2 for the Re(I) tricarbonyl bipyridyl complex ReL2 which displayed enhanced emission intensity in the cis form.2PA is also of interest for biological applications due to the longer, less damaging wavelengths used at which biological tissue is more transparent. Photodynamic therapy (PDT) is a non-invasive clinical treatment for cancers where a photosensitizer is optically excited to generate cytotoxic singlet oxygen, which kills cells in the area under irradiation. Platinum group transition metal complexes have been investigated for this purpose due to their strong 2PA properties and accessible low-lying triplet states, which make them efficient triplet-triplet energy transfer agents. A new cyclometallated Ir(III) complex bearing a fluorenyl phenanthroline ligand and a related bimetallic Ir(III)-Ru(II) complex were synthesised and assessed as two-photon singlet oxygen sensitizers. The monometallic Ir(III) complex was also shown to demonstrate PDT action by altering the morphology of C6 Glioma cells under 740 nm two-photon excitation.

Thesis (M.S.)--Rochester Institute of Technology, 1986. / Typescript. Includes bibliographical references (leaves 43-44).